<igtab:UltraWebTab ID="tabSource" runat="server" AsyncMode="On">
            <ClientSideEvents BeforeAsyncSubmit="UltraWebTab1_BeforeAsyncSubmit" />
            <Tabs>
                <igtab:Tab Key="UP" Tag="Upload" Text="Upload">
                    <ContentTemplate>
                        <table>
                            <tr>
                                <td>
                                    <asp:FileUpload ID="FileUpload1" runat="server" />
                                    <asp:Button ID="btnUpload" runat="server" OnClick="btnUpload_Click" Text="Upload" />
                                </td>
                            </tr>
                        </table>
                    </ContentTemplate>
                </igtab:Tab>
                <igtab:Tab Key="AB" Tag="Tab AB" Text="TabAB">
                    <ContentTemplate>
                        SIMPLE TEXT
                    </ContentTemplate>
                </igtab:Tab>
            </Tabs>
        </igtab:UltraWebTab>

Then here's the client side script

<script type="text/javascript">
function UltraWebTab1_BeforeAsyncSubmit(oWebTab, notUsed, oEvent, id)
{
    // if async postback was triggered by
    // btnUpload then trigger full postback
    if(id.indexOf('btnUpload') > 0)
    {
        oEvent.fullPostBack = true;
    }
}
</script>

Then the code behind

    protected void Page_Load(object sender, EventArgs e)
    {
    }

    protected void btnUpload_Click(object sender, EventArgs e)
    {
        string path = @"C:\temp\" + FileUpload1.FileName;
        FileUpload1.SaveAs(path);
    }

 When fullPostback is set to true in BeforeAsyncSubmit, the page postsback as expected but the button's click event handler doesn't run. My goal is to support file upload inside a web tab and without setting the fullPostBack the button click event fires but as we know, the FileUpload will have no relevant data/content.